Method for knock regulation in an internal combustion engine

ABSTRACT

A method for knock control of an internal combustion engine, a knock detection being carried out on the cylinders of the internal combustion engine and a moment of ignition being retarded by a specifiable value as a function of detected knocking combustion in at least one of the cylinders, the system including at least two evaluation electronics and at least one cylinder being assigned to each of these evaluation electronics, and the knock sensor signals assigned to the cylinders being evaluated by the evaluation electronics assigned in each case, and the knock detection and the specification of the moment of ignition being effected by a control electronics, and the evaluation electronics being monitored for functionality. It is provided that, upon detection of a malfunction of at least one of the evaluation electronics, the at least one cylinder assigned to this evaluation electronics is linked to the control of at least one cylinder having intact evaluation electronics.

FIELD OF THE INVENTION

The present invention relates to a method for knock control in aninternal combustion engine.

BACKGROUND INFORMATION

Carrying out a so-called knock control in internal combustion engines isknown in the art. In so doing, a combustion process in the cylinders ofthe internal combustion engine is monitored for knocking combustion.Knocking combustion is identified by characteristic vibrations that maybe detected using so-called knock sensors which are mounted on thehousing of the internal combustion engine. Knocking combustion is, forexample, a function of the quality of a fuel being used, the compressionof the fuel/air mixture in the cylinders and/or the moment of ignition.The ignition timing is retarded by a specifiable amount as a function ofthe detected knocking combustion. Since retarding the ignition timingleads to loss of torque and increased fuel consumption, running theinternal combustion engine as close as possible to a so-called knocklimit is known in the art. The knock control in this case runs theinternal combustion engine as close as possible to the knock limit.Here, the ignition timing is controlled according to the actual signalsdetermined by the knock sensors.

Detecting knock using knock sensors, which are typically designed asstructure-borne noise sensors, is known in the art. The use of ioniccurrent sensors or pressure sensors is also conceivable. At least onecylinder of the internal combustion engine is assigned to each of theseknock sensors. The control unit has two evaluation electronics to whichthe sensors are assigned, and by which the sensor signals are evaluatedin a cylinder-specific manner. The evaluation circuit supplies theresult of the preprocessed sensor signals to a control electronics,which typically is integrated within an engine control unit. Here,knocking of the individual cylinders is detected, and the ignition angleretard and moment of ignition are calculated.

During normal use of the knock control, the evaluation electronics arecontinually monitored for correct functioning by a diagnostic. If amalfunction is determined, the system automatically switches to safetyknock control to prevent damage to the internal combustion engine. Thissafety knock control provides that of a safety retard of the ignitiontiming is implemented for all cylinders of the internal combustionengine. However, in this context, it is disadvantageous that wheneverthe moment of ignition, and thus the ignition angle, is retarded awayfrom the optimal ignition angle, the efficiency and the power output ofthe internal combustion engine are reduced, thereby increasing fuelconsumption. In turbo-charged internal combustion engines, retarding themoment of ignition may cause the charging-air pressure to drop, whichcan lead to power losses of up to 40%.

SUMMARY OF THE INVENTION

The method according to the present invention offers the followingadvantage: in the event of a failure or malfunction of an evaluationelectronics of the knock control, a safety retard of the moments ofignition is not necessary for all cylinders of the internal combustionengine. Since, upon detecting a malfunction of at least one of theevaluation electronics, the at least one cylinder assigned to thisevaluation electronics is linked to the control of at least one cylinderwith intact evaluation electronics, all cylinders of the internalcombustion engine are advantageously not automatically switched to themaximum safety retard, but rather the at least one cylinder to which themalfunctioning evaluation electronics circuit is assigned is guided byanother cylinder of the internal combustion engine whose evaluationelectronics is in working order. This ensures that the cylinders withoperational evaluation electronics may still be operated using anoptimal moment of ignition, while only the at least one cylinder withmalfunctioning evaluation electronics is operated with retarded ignitiontiming which, however, is below the previously known safety ignitionretard. The overall result is that the efficiency of the internalcombustion engine is only insignificantly impaired. In particular, thisguidance of the cylinder having defective evaluation electronics makesit possible to operate the cylinder close to its knock limit even if itsevaluation electronics malfunction.

If an evaluation electronics circuit fails, a guide cylinder function isactivated for the cylinders assigned to this evaluation electronics.This means that the cylinders of the defective evaluation electronicsare guided by cylinders of an intact evaluation electronics. The centralcontrol electronics (engine control unit) detects knocking, chooseswhich cylinders assume guidance of the cylinder assigned to the failedevaluation electronics, and calculates the resulting ignition retard.Only if all evaluation electronics are detected as defective is auniform safety ignition retard activated for all cylinders.

For the guide cylinder function, at least one cylinder of an intactevaluation electronics is selected as the guide cylinder. The ignitionangle settings of the at least one guided cylinder are derived fromthose of the at least one guide cylinder. This preferably results inseveral possibilities. Thus, an ignition angle setting of the guidedcylinder may be the same as the ignition angle of the guide cylinder.Furthermore, it is preferred if the ignition angle setting of at theleast one guided cylinder corresponds to an ignition angle setting ofthe at least one guide cylinder plus a safety offset (timing retard awayfrom the knock limit).

Another preferred embodiment of the present invention provides that theretard of the ignition angle for the at least one guided cylinder ismade in one step following a knock event at the guide cylinder.Furthermore, it is preferred if the retard for the at least one guidedcylinder is effected in several small steps following a knock event inthe at least one guide cylinder.

Finally, it is preferable if the cylinder which uses the greatest retardof the ignition timing is established as the guide cylinder. Finally, itis also preferred if, during initialization of the control electronicsand the evaluation electronics, respectively, it is determined whichcylinders may be used as the guide cylinder in the particular groupsassigned to an evaluation electronics.

BRIEF DESCRIPTION OF THE DRAWING

The drawing schematically shows a knock control of an internalcombustion engine.

DETAILED DESCRIPTION

The figure schematically shows an internal combustion engine 10, thatincludes a total of four cylinders 12, 14, 16 and 18. A knock sensor 20,22, 24 and 26 is assigned to each of cylinders 12, 14, 16 and 18. Theknock sensors detect structure-borne noise vibrations that are caused bycombustion in cylinders 12, 14, 16 and/or 18. Knock sensors 20, 22, 24,26 are connected to evaluation electronics 30 and 32. In this context,evaluation electronics 30 is assigned to knock sensor 20 and knocksensor 22, and evaluation electronics 32 is assigned to knock sensor 24and knock sensor 26. Evaluation electronics 30 and 32 are implementedusing either digital, analog or mixed technology. Evaluation electronics30 or 32 are integrated within an engine control unit 28 to which arefed the signals supplied and preprocessed by knock sensors 20, 22, 24,26. Engine control unit 28 includes, among other things, at least onemicroprocessor 33 and at least one memory medium 34 in which controlalgorithms for components 36 that influence the combustion in cylinders12, 14, 16 and 18 are stored. Components 36 are, for example, finalcontrolling elements for adjusting an ignition of internal combustionengine 10.

A diagnostic module 38 is assigned to evaluation electronics 30 and 32and permanently monitors the functionality of evaluation electronics 30and 32 during their specified use. Diagnostic module 38 is implementedin engine control unit 28. The diagnostic module may be implementedphysically by the at least one microprocessor 33 that processes anappropriate routine.

The knock control schematically depicted in the Figure illustrates thefollowing function:

During the operation of internal combustion engine 10, the combustion inindividual cylinders 12, 14, 16 and 18 is continually monitored viaknock sensors 20, 22, 24 and 26. According to structure-borne vibrationspicked up in this context, a control parameter is specified forcomponents 36 via evaluation electronics 30 and 32 and data control unit28, so that knocking combustion in cylinders 12, 14, 16 and 18 issuppressed. Using the control parameters, cylinders 12, 14, 16 and 18 inthis case are operated close to their knock limit.

Evaluation Electronics 32 and 34 are continually monitored forfunctionality by diagnostic module 38 (control unit 28). If there is amalfunction, for example, in evaluation electronics 30, it is detectedby diagnostic module 38. Then diagnostic module 38 causes a guidecylinder function to be activated for the knock control of cylinders 12,14. In this way, cylinders 12, 14 are guided by the cylinders assignedto evaluation electronics 32. Due to this measure, cylinders 16 and 18continue to be operated with optimum knock control via evaluationelectronics 32. Simultaneously, a guide cylinder function is activatedfor the knock control of cylinders 12, 14 so that they also continue tobe operated in knock-controlled fashion. The overall result is thatcylinders 16 and 18 are run with optimal knock control, while cylinders12 and 14 may be operated relatively close to their knock limit, despitea defect in evaluation electronics 30, assigned to them. Cylinders 12and 14 are thus guided by cylinders 16 and 18. Due to this guidance,none of cylinders 12, 14, 16 and 18 of internal combustion engine 10have to be driven using the safety retard of the ignition timing and besubject to the related previously-mentioned disadvantages. The overallresult is a clear improvement in power output and efficiency of internalcombustion engine 10 when evaluation electronics 30 is defective.

According to additional exemplary embodiments (not shown), each ofcylinders 12, 14, 16 and 18 may obviously be assigned its own evaluationelectronics that may correspondingly be switched over in the event of afault. Also, for internal combustion engines 10 that have more then fourcylinders, corresponding cylinder groups may each be assigned to anevaluation electronics.

Furthermore, it may be provided that not every cylinder 12, 14, 16, 18is monitored via its own knock sensor 20, 22, 24, 26. In this case, oneknock sensor may also be assigned to a plurality, for example, twocylinders.

What is claimed is:
 1. A method for knock control of an internalcombustion engine, comprising: performing a knock detection on cylindersof the internal combustion engine, a knock sensor signal being producedfor each cylinder; retarding a moment of ignition by a specifiable valueas a function of a detected knocking combustion in at least one of thecylinders; causing at least two evaluation electronics to evaluate theknock sensor signals, at least one of the cylinders being assigned toeach of the at least two evaluation electronics; causing a controlelectronics to effect the knock detection and a specification of themoment of ignition; monitoring a functionality of the at least twoevaluation electronics; and upon a detection of a malfunction of atleast one of the at least two evaluation electronics, linking the atleast one cylinder assigned to the at least one evaluation electronicswith the malfunction to a control of at least one of the cylindersassigned to an intact one of the at least two evaluation electronics. 2.The method as recited in claim 1, further comprising: in the event of afailure of one of the at least two evaluation electronics, those of thecylinders assigned to the failing evaluation electronics are guided bycylinders associated with another one of the at least two evaluationelectronics.
 3. The method as recited in claim 1, wherein: at least oneof the cylinders includes a guide cylinder and remaining ones of thecylinders are guided cylinders, and from one of an ignition angle and atiming retard of the guide cylinder, the ignition angle is specifiedfrom which ignition angles of the guided cylinders are derived.
 4. Themethod as recited in claim 3, wherein: the one of the ignition angle andthe timing retard of the guide cylinder is used for the guidedcylinders.
 5. The method as recited in claim 1, wherein: one of thecylinders is a guide cylinder, remaining ones of the cylinders areguided cylinders, and a retard of an ignition angle is effected for theguide cylinder and for the guided cylinders in response to a knock eventin a guide cylinder.
 6. The method as recited in claim 5, wherein: oneof the cylinders is a guide cylinder, remaining ones of the cylindersare guided cylinders, and a safety offset is applied away from a knocklimit to an ignition angle of the guide cylinder to determine ignitionangles of the guided cylinders.
 7. The method as recited in claim 5,further comprising: retarding an ignition timing of the guided cylindersin a plurality of small steps following the knock event in the guidecylinder.
 8. The method as recited in claim 5, further comprising:retarding an ignition timing of the guided cylinders in a single stepfollowing the knock event in the guide cylinder.
 9. The method asrecited in claim 5, wherein: the guide cylinder corresponds to one ofthe cylinders that has one of a largest, a smallest, and an averageretard of the ignition angle of the guide cylinder.
 10. The method asrecited in claim 5, wherein: the guide cylinder includes one of thecylinders that is determined in an initial setting of the ignitionsystem.